How Daylighting Devices Work


A cross-section of a daylighting device installation
A cross-section of a daylighting device installation
(c) Solatube International, Inc.

There's nothing quite like being stuck inside a building on a nice day. If you could just get outside, you could enjoy the sunlight instead of the glow of fluorescent or incandescent light bulbs. If you're lucky, you sit near a window and can get some of the benefits that way. But if you're not close to a window, your situation might seem pretty bleak. There's just no substitute for the light of the sun.

That's one reason many architects are looking into ways to maximize natural lighting within buildings. But the reasons go beyond psychological effects. Sunlight is clean energy -- it reduces the need to use lighting solutions that require ele­ctricity. It's also free. A free, clean lighting source that helps people stay motivated and happy sounds too good to be true.

In fact, there are a few problems that come along with natural lighting. One is that it depends entirely on the sun's schedule -- once night falls, you're out of luck. Sunlight isn't constant -- as the day progresses, windows or skylights will receive more or less sun. Another problem is that the sun's position in the sky changes slightly during different parts of the year. A window that gets a lot of sunlight during the summer months may not receive as much in the winter. And it's not like you continually can change the position of windows or skylights to compensate for the sun's position.

­That's where daylighting devices come in. Basically, a daylighting device is an object that collects, transmits and emits daylight into a building or other structure. A building with daylighting devices can use sunlight to provide a natural alternative to electric lighting eve­n in rooms that have no windows.

Daylighting devices give architects more flexibility compared to skylights -- the part of the device that collects sunlight doesn't have to be directly above the room you want to light. Even if the section of roof above the room in question is normally in shadows, you have options. A daylighting device can collect light from a sunny part of the roof and transmit it to nearly any room.

It sounds a bit like magic, but it's all based on some fairly simple scientific principles. We'll take a look at the basic parts of a daylighting device and find out how they work together in the next section.

Parts of Daylighting Devices

This illustration shows how the SolaTube daylighting device captures and transmits sunlight into a light panel inside a house.
This illustration shows how the SolaTube daylighting device captures and transmits sunlight into a light panel inside a house.

The three basic parts of a daylighting device are a light-collecting device, a light-transmitting device and a light emitting device. That's a fancy way of saying daylighting devices use a series of lenses and mirrors (or optic fibers) to transmit sunlight into a building.

The lenses in the light collection part of a daylighting device direct light into the light transmission component. This part of the device often has a glass dome or pyramid on top of it. The glass directs light into the device's lenses. Some daylighting devices use a pair of lenses. The first lens is a convex lens, which refracts light toward a central point. Beneath the convex lens is a concave lens. Concave lenses reflect light rays outward toward the light transmission part of the device.

­The transmission portion of a daylighting device is either a tube with a reflective interior or a series of optical fibers. An optical fiber is essentially a miniaturized reflective tube, so, in general, both solutions use the same approach. As light enters the tube or fiber, it hits the reflective inner surface and bounces farther down the path. It continues to do this until it hits the light emitter section of the daylighting device. The longer the transmission section of a daylighting device, the less light will make it to the emitter. In other words, ru­nning a tube down a 60-story building to light the basement may not be the best solution.

The light emitter is the part of the device that you'd see if you were inside the building. It's the equivalent to a fluorescent light panel or an incandescent bulb. Many emitters have a special lens that diffuses light. A diffuse lens has tiny surfaces within it that reflect light in different directions. The end effect is that the lens spreads the light around.

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­Daylighting devices have a few advantages over windows and skylights. One is that they aren't affected by the position of the sun. The amount of light that passes through a window or skylight can change dramatically as the day goes on. But as long as the light-catching section of a daylighting device receives sunlight, the emitter will continue to give off light; although the brightness may vary a little depending on the intensity of the sun. Another advantage is that you can put the light-catching part of the daylighting device in any location on a roof and use the transmission tube or fibers to run the light to its destination. You can even bend light around corners. And you don't have to sit near an exterior wall to enjoy the benefits of a daylighting device the way you do with a window.

Daylighting devices shouldn't be the sole source of lighting for a building. A daylighting device won't do you much good if you need light past sundown. While some daylighting devices can cap­ture ambient light even on cloudy days, you'll probably notice a decrease in performance when skies are overcast. Daylighting devices work best as a supplemental light source.

Benefits of Daylighting Devices

Sunlight brightens a dining room.
Sunlight brightens a dining room.

One of the biggest benefits to daylighting devices involves your mood. If you aren't getting enough exposure to sunlight you could develop seasonal affective disorder (SAD). The symptoms of SAD include fatigue, social withdrawal, a decreased sense of interest in activities and even weight gain. SAD can even turn into full-blown depression. According to the American Psychiatric Association (APA), SAD develops when there's a biochemical imbalance in the brain as a result of decreased exposure to sunlight. Sunlight also inhibits melatonin production, a hormone that is related to sleep. Your body produces more melatonin on dark days or days when you don't get enough sunlight.

While most people develop symptoms of SAD during the late fall and into the winter months, it's possible to suffer from SAD any time of the year. If you spend most of time indoors and away from the sun, you could suffer from SAD even in the middle of summer. The APA suggests a walk outside on a sunny day as a way to treat SAD symptoms.

A daylighting device can help keep your exposure to sunlight steady throughout the year. Business owners may find that their employees are more productive and happier with increased sunlight exposure.

Some tasks may actually be easier when performed in sunlight than with other lighting methods. A Cornell University study compared fatigue levels between two groups of students. Each group of students was told to study or do coursework for four hours over the course of four days. The researchers used two different lighting sources during the experiment. One room used normal "cool white" fluorescent bulbs. The other room had a special kind of fluorescent bulb that produced the same light wavelengths as sunlight. The students were not aware of the purpose of the experiment and didn't know about the two different kinds of bulbs. The researchers found that while the students didn't report any significant subjective differences between one day and the next, they did perform visual acuity tasks better on the days when they were exposed to the special fluorescent bulbs.

­Daylighting devices are also a good way to cut back on energy consumption. As the green movement sweeps the globe, more companies and individuals are looking for ways to reduce their carbon footprints. If you use natural lighting, not only will you reduce your need for electricity, but also cut back on the physical waste you create -- you won't have to replace light bulbs as often. If the sun burns out, the lighting in your living room will be the least of your worries.

Reduced energy consumption also means reduced electricity bills. So not only is it environmentally friendly to use natural lighting, it can be fiscally responsible, too! Just remember that there's a significant investment you'll need to make up front if you decide to adopt daylighting devices.

Next, let's look more closely at how much it costs to purchase and install a daylighting device.

The Cost of Daylight

Companies like SolaTube offer daylighting devices for residential homes, commercial businesses and even schools.
Companies like SolaTube offer daylighting devices for residential homes, commercial businesses and even schools.

So how much do daylighting devices cost? The honest answer is that it all depends on what you need and the vendor you use. Solatube offers several models of daylighting devices for homeowners and professionals. In addition to the basic devices, the company produces specialized diffusers, roof mounts, effect lenses, dimmer switches and light kits. The light kits allow you to mount an incandescent bulb in the daylighting device to provide light from the same fixture after the sun goes down.

The price of the daylighting device changes as you add more options. It also increases as the length of the transmission tube increases. If you only need a couple of feet of tubing, you'll spend much less than someone who needs 20 feet (6.1 meters) or more. In addition, if you need special tube sections to work your way around obstacles like support beams, you can bet that it's going to cost you extra.

On top of the parts cost are the installation fees. Solatube claims that most professionals can install a daylighting device within a couple of hours. Do-it-yourselfers might need a full day to put a daylighting device in place. Either way, you're going to incur some installation costs. You'll need to pay for labor or you'll need to invest in the right tools to put a device together.

To give you an idea of how much a daylighting device can cost we'll look at an example. Solabrite, a Solatube dealer, offers two Solatube daylighting device models for homeowners. They sell the 10-inch (25.4 centimeter) Solatube 160 DS for $649. The 290 DS, which is 14 inches (35.6 centimeters) in diameter, goes for $749. For both models, the price includes up to four feet of transmission tube. Longer tubes will cost more. If you want a daylight dimmer, that option will add $325 to $335 to the price tag, depending on the model. Prices include installation fees. If you want to tackle the project on your own, the cost is significantly lower.

This illustration shows how SolaTube's butterfly dimmer device can limit the light coming into your house. This illustration shows how SolaTube's butterfly dimmer device can limit the light coming into your house.
This illustration shows how SolaTube's butterfly dimmer device can limit the light coming into your house.

­According to Solatube, one cost you won't have to worry about is replacing your furniture. The ultraviolet rays in sunlight can cause fabric colors to fade after prolonged exposure. But the lenses and diffuser in Solatube's devices filter out most of the UV radiation. While you'll get the benefit of sunlight exposure, you won't have to worry about colors fading or getting a sunburn.

The initial installation expenses may be worth it if your electricity bills are high. You won't have to purchase light bulbs as often, reducing costs even further. It may take a few months or longer to pay off the purchase, but ultimately daylighting devices will pay for themselves. And you'll be reducing your carbon footprint in the process!

As the green movement continues to gather support, we'll likely see more lighting solutions that take advantage of natural source­s. Who knows? In a few years, we may all be enjoying the benefits of sunlight even if we spend most of our time indoors.

To learn more about daylighting devices and related topics, take a look at the links on the following page.

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More Great Links

Sources

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